Esophageal stent

ABSTRACT

A radially self-expanding stent particularly suited for treating esophageal strictures, includes a medial region and proximal and distal cuffs having diameters greater than the medial region diameter when the stent is in the relaxed state. A silicone coating circumscribes the medial region, but the cuffs are not coated and retain their open weave construction. As a result, the cuffs remain particularly well suited to immediately contact esophageal wall tissue and resist stent migration, while the silicone coated medial region provides a barrier to tumor ingrowth, and has an enhanced radial restoring force to maintain an open passageway in the esophagus. A deployment device for the stent includes an interior catheter surrounded by the stent and having an esophageal dilation feature, along with an exterior catheter that radially compresses the stent. A low durometer sleeve, fixed to the interior tube and in surface engagement with the compressed stent, tends to fix the axial position of the stent relative to the interior catheter whenever the exterior catheter is moved axially relative to the inner catheter. Consequently, precision in stent placement and the ability to recapture a partially deployed stent are enhanced.

This is a continuation of Ser. No. 221,459 filed Apr. 1, 1994 nowabandoned which is a cont. of Ser. No. 07/880,435, filed on May 8, 1992,now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to body implantable treatment devices, andmore particularly to stents and other prostheses intended for fixationin body lumens especially including the esophagus.

Carcinomas in the esophagus lead to progressive dysphagia, i.e.difficulty in swallowing, and the inability to swallow liquids in themost severe cases. While surgical removal is sometimes effective, themajority of patients have tumors that can not be surgically removed.Repeated dilations of the esophagus provide only temporary relief.

Difficult or refractory cases often are treated by intubation usingrigid plastic prostheses, or laser therapy with an Nd:YAG laser. Thesetechniques, while often effective, have disadvantages. Rigid plasticprotheses are large, for example having a diameter of 10-12 mm andlarger (25-29 mm) outer end flanges. Placement of rigid plastic stentsis traumatic, and too frequently causes perforation of the esophagealwall. These protheses further are subject to migration, obstruction withfood or tumor ingrowth, and late pressure necrosis.

Laser therapy is expensive, typically requiring several treatmentsessions. Tumor recurrence is frequent, in the range of 30-40 percent.Submucosal tumors, and certain pulmonary and breast tumors causingdysphagia by esophageal compression, can not be treated by lasertherapy.

The search for a more suitable prosthesis has lead to experiments withGianturco stents, also known as Z-stents. U.S. Pat. No. 4,800,882(Gianturco) describes such a device employed as an endovascular stent.Such stents for the esophagus have been constructed of 0.018 inchstainless steel wire, and provided with a silicone cover to inhibittumor ingrowth. It was found necessary, however, to provide a distalsilicone bumper to prevent trauma to the esophageal mucosa.

Self-expanding mesh stents also have been considered for use asesophageal prostheses. U.S. Pat. No. 4,655,771 (Wallsten) discloses amesh stent as a flexible tubular braided structure formed of helicallywound thread elements. Mesh stents appear unlikely to lead to pressurenecrosis of the esophageal wall. With its inherent pliability the meshstent, as compared to a rigid plastic stent, is insertable with muchless trauma to the patient. Further, the stent can mold itself to andfirmly fix itself against the esophageal wall, to resist migration.However, the stent is subject to tumor ingrowth because of the spacesbetween adjacent filaments.

A further difficulty with self-expanding stents, concerns their accurateplacement and deployment. Typically a tube surrounds the self-expandingstent and radially compresses the stent into a reduced-radius deliveryconfiguration. With the stent positioned at a treatment site, the outertube is axially withdrawn, permitting the stent to radially self-expand.However, the larger size of an esophageal stent (as compared to biliaryand vascular applications, for example) gives rise to substantialfriction at the stent/outer tubing interface. As a result, it isdifficult to precisely maintain the position of the stent duringdeployment, and practically impossible to retract the stent afterpartial deployment.

Therefore, it is an object of the present invention to provide a stentdelivery device including exterior tubing surrounding the stent andmovable axially to release the stent for radial self-expansion without atendency in the stent to follow the axial movement of the exteriortubing.

Another object is to provide a stent deployment device capable ofretracting a radially self-expanding stent for repositioning of thestent, even though the stent has been partially deployed and is radiallyexpanded over the majority of its axial length.

Another object is to provide a device for delivering and deploying aprostheses to a treatment site within a body lumen, with means fordilating the body lumen at the treatment site prior to stent deployment.

A further object of the invention is to provide a radiallyself-expanding stent including a freely radially self-expanding fixationregion in combination with a barrier region to inhibit tumor ingrowth.

Yet another object is to provide an esophageal prostheses deployablewith reduced trauma to the patient, having more resistance to migration,and providing a barrier to tumor ingrowth as effective as conventionalrigid plastic prostheses.

To achieve these and other objects, there is provided an apparatus fordeploying a radially self-expanding stent within a body lumen. Theapparatus includes a stent confining means for elastically compressing aradially self-expanding stent into a delivery configuration in which theself-expanding stent has a reduced radius along its entire axial length.The apparatus includes an elongate and flexible stent delivery devicehaving a proximal end, a distal end and a distal region near the distalend. The distal region is used in delivering the radially self-expandingstent into a body lumen, and in positioning at a treatment site withinthe body lumen with the stent surrounding the delivery device along thedistal region. The proximal end of the delivery device remains outsideof the body. An axial restraining means is disposed along the distalregion of the delivery device. A control means is operably associatedwith the delivery device and the confining means. The control meansmoves the confining means axially relative to the delivery device towardand away from a confinement position in which the confining meanscompresses the self-expanding stent into the delivery configuration, andurges the stent into a surface engagement with the axial restrainingmeans. The restraining means, due to the surface engagement, tends tomaintain the self-expanding stent axially aligned with the deploymentdevice as the confining means is moved axially away from the confinementposition to release the stent for radial self-expansion.

Preferably the stent delivery device is an elongate and flexible lengthof interior tubing, with a central lumen for accommodating a guidewire.The stent confining means can be an elongate and flexible length oftubing, having a lumen for containing the interior tubing. The second(or outer) tubing surrounds the stent to confine it.

The preferred axial restraining means is a low durometer sleevesurrounding the interior tubing along the distal region. If desired, anadhesive can be applied to an exterior surface of the sleeve.Alternatively, the axial restraining means can consist of severalelongate strips disposed along the distal region, with adhesive appliedto radially outward surfaces of the strips, if desired.

In either event, so long as the exterior tubing surrounds the stent toradially compress the stent, it also maintains the stent in surfaceengagement with the sleeve or strips. As the exterior tubing is axiallywithdrawn to allow part of the stent to radially self-expand, the restof the stent remains confined against the sleeve or the strips. As aresult, the stent does not travel axially with the exterior tubing.Rather, the stent remains substantially fixed in the axial directionwith respect to the interior tubing. This structure affords severaladvantages. First, the interior tubing can be used as a means topositively maintain the radially self-expanding stent in the desiredaxial position during deployment. The interior tubing can itself beemployed as a reliable indicator of stent position, both prior to andduring deployment. Further, should the need arise to retract the stentafter a partial deployment, the outer tubing can be moved back into theconfinement position, without tending to carry the stent along with it.

Another aspect of the present invention is a device for fixation in abody lumen. The device includes a tubular stent of open weaveconstruction having a predetermined normal configuration. The stent isradially compressible to a reduced-radius configuration to facilitate anaxial insertion of the stent into a body lumen for delivery to atreatment site within the body lumen. A continuous film is formedaxially along the stent and circumscribes the stent over a barrierregion of the stent. The continuous film substantially prevents growthof tissue through the stent along the barrier region. A portion of thestent is substantially free of the continuous film to provide a fixationregion of the stent for positively fixing the stent within the bodylumen at the treatment site. Fixation is achieved by radial expansion ofthe stent into a surface engagement with a tissue wall segment definingthe body lumen.

The preferred stent comprises a mesh formed of braided helical strands.The fixation region can comprise a proximal cuff and a distal cuff, withthe barrier region being a medial sleeve of the stent positioned betweenthe cuffs. Also, the barrier region preferably has a diameter less thanthe fixation region diameter when the stent is in its normal or relaxedconfiguration. A preferred material for the film is silicone. Whenproperly controlled as to thickness, the silicone film provides agradual self-expansion. More particularly, while the fixation regionself-expands virtually instantaneously upon release of the stent, themedial barrier region, upon encountering a tumor or other striction, cantake up to 24 hours to achieve a substantially complete radialself-expansion against the tumor.

This feature is particularly advantageous in connection with treatingesophageal strictures, where tissue at the stricture may be severelyweakened, and where normal convulsions of the esophagus tend to causestent migration. More particularly, the rapidly expanding fixationregions contact normal esophageal tissue on either side of a stricture,and are sufficiently pliable to adjust to esophageal convulsions.Meanwhile, the barrier region of the stent experiences a gradual radialexpansion, thus causing minimal disruption to tissue along thestricture.

A further feature of the invention is a system for treating a stricturewithin a body lumen. The system includes a radially self-expandingstent, and an elongate and flexible stent delivery device having aproximal end and distal end. The device further has a distal region fordelivering the radially self-expanding stent into the body lumen andpositioning the stent at a treatment site within the body lumen, withthe stent surrounding the delivery device along the distal region. Afirst elongate and flexible length of tubing, having a lumen running thelength of thereof, contains the stent delivery device within the lumen.The first tubing also elastically compresses the stent into a deliveryconfiguration in which the stent has a reduced radius along its entireaxial length. The first tubing is movable proximally relative to thedelivery device and the stent, to allow the stent to radiallyself-expand into a surface engagement with body tissue defining thelumen. A distal tip is provided at the distal end of the stent deliverydevice for initially dilating a stricture at the treatment site. Anenlargement feature is provided near the distal end of the stentdelivery device. The enlargement feature has a diameter substantiallyequal to an interior diameter of the first tubing. The enlargementfeature further has a distal transition region that diverges proximallyfrom the tip to a mid-portion of the enlargement feature. The transitionregion further dilates the stricture to facilitate a positioning of thedistal region of the first tubing along the stricture.

Preferably the distal region of the delivery device has a diameter lessthan the diameter of the enlargement feature mid-portion, and theenlargement feature further includes proximal transition region thatconverges in the proximal direction from the enlargement featuremid-portion. The proximal transition region facilitates withdrawal ofthe delivery device after deployment of the stent.

Thus, in accordance with the present invention, a radiallyself-expanding stent can be positioned accurately at a desired treatmentsite within a body lumen, based on an accurate positioning of theinterior tubing or other stent delivery means. The stent may be allowedto radially self-expand over the majority of its axial length, and yetbe retracted if necessary or desired, all while its axial position withrespect to the delivery tool is maintained.

IN THE DRAWINGS

For a further appreciation of the above and other features andadvantages, reference is made to the following detailed description andto the drawings, in which:

FIG. 1 is a side elevational view of a stent deployment deviceconstructed in accordance with the present invention;

FIG. 2 is an end elevation of the device;

FIG. 3 is a sectional view taken along the line 3--3 in FIG. 2;

FIG. 4 is a side elevation of the stent in a relaxed configuration;

FIGS. 5-8 are sectional views similar to FIG. 3, showing the device atseveral stages of deploying a radially self-expanding stent;

FIG. 9 is a sectional view taken along the line 8--8 in FIG. 3, showinga stent retaining layer;

FIG. 10 is a sectional view similar to FIG. 9, but showing analternative embodiment device utilizing stent retaining strips in lieuof the retaining layer shown in FIG. 9;

FIG. 11 is a schematic view of an esophageal prosthesis constructed inaccordance with the present invention;

FIGS. 12 and 13 illustrate alternative braid angle configurations forself-expanding prostheses;

FIG. 14 is a side elevational showing a mandrel used in forming theprosthesis of FIG. 11;

FIG. 15 schematically illustrates the prostheses of FIG. 11 in anesophagus, a short time after its deployment;

FIG. 16 schematically illustrates the prosthesis one day after itsdeployment; and

FIG. 17 illustrates an alternative prostheses constructed according tothe present invention, and deployed in an esophagus, with a distal endof the prostheses protruding into the stomach.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, there is shown in FIG. 1 a deploymentdevice 16 for delivering a stent or other prostheses to an intendedfixation location within a body cavity, and then controllably releasingthe stent for radial self-expansion to a fixation within the bodycavity.

The device includes an elongate exterior catheter or tubing 18constructed of a biocompatible polymer, e.g. polypropylene, FEP orTeflon, with an outside diameter of about 12 mm or less. A central lumen20 runs the length of catheter 18. On the outside of catheter 18 arevisible markings 22 designating cm. When using the device, e.g. indeploying a radially self-expanding prostheses within the esophagus, aphysician can determine the extent of insertion into the esophagus basedupon these markings. Throughout deployment, the proximal end of exteriorcatheter 18 remains outside the patient. A hub or handle 24 at theproximal end of the exterior catheter, facilitates manipulation ofexterior catheter 18 by hand.

An interior catheter or tubing 26 runs through lumen 20, containedwithin the exterior catheter. Interior catheter 26 has an outsidediameter of approximately 6 mm or less, and is constructed of abiocompatible polymer, e.g. polypropylene, FEP, Hytrel or nylon.

At the distal end of interior catheter 26 is a distal tip 28. The distaltip is flexible, yet sufficiently rigid to be self-supporting ratherthan pliable when encountering tissue. As a result, distal tip 28 can beused to dilate the esophagus along regions where a tumor or otherstricture is present. Over the majority of its length, distal tip 28 hasa diameter substantially equal to the interior tubing diameter, with adistal converging end 30 formed as part of the tip.

A proximal region 32 of interior catheter 26 extends proximally beyondhub 24. Visible markings on the outer surface of catheter 26 definethree adjacent segments of the proximal region, as indicated at 34, 36and 38, respectively. These segments can be different colors if desired,to enhance their recognition. These segments, and more particularly theposition of hub 24 along them, indicate the axial position of exteriorcatheter 18 relative to interior catheter 26. The segments furtherindicate the stages of stent deployment, as is later explained.

At the proximal end of interior catheter 26 is a hub or handle 40, whichfacilitates manipulation of the interior catheter by hand. A lumen 42(FIG. 3) runs the length of interior catheter 26, to accommodate aguidewire 44.

FIG. 3 reveals further features of interior catheter 26, including adistal enlargement feature 46 positioned just proximally of tip 28.Enlargement feature 46 is cylindrical, and includes a mid-portion ormedial region 48 having an outside diameter of about 11-12 mm,substantially equal to the diameter of lumen 20. Thus the enlargementfeature is in surface engagement with exterior catheter 18 as shown inFIG. 3, and can slide relative to the exterior catheter.

Enlargement feature 46 also includes proximal and distal transitionregions at 50 and 52, respectively. Distal transition region 52 divergesproximally from the distal tip to the mid-portion of the enlargementfeature. The proximal transition region converges proximally from themid-portion to the interior catheter.

An annular restraining sleeve 54 surrounds a distal region 56 of theinterior catheter. The sleeve is formed by wrapping double sidedadhesive tape around the interior catheter so that the sleeve adheres tothe inner catheter and also exhibits a tackiness over its exteriorsurface. Radiopaque markers 58, 60, 62 and 64 surround the sleeve. Thesemarkers can be surrounded by sleeve 54 if desired.

Surrounding sleeve 54 is a radially self-expanding stent 66. The stentpreferably is of open weave or mesh construction, formed of multiplehelically wound strands or filaments of a flexible material such as bodycompatible stainless steel. The durometer of sleeve 54 is substantiallyless than the durometer of catheters 18 and 26. Retaining sleeve 54 issized such that whenever exterior catheter 18 radially compresses stent66, the catheter also is pressing the stent into a surface engagementwith the retaining sleeve, to the point of at least slightly elasticallydeforming the sleeve. As a result, friction between the stent and sleeve54 substantially exceeds friction between the stent and the interiorsurface of catheter 18. Given the length and positioning of retainingsleeve 54, stent 66 when compressed contacts the sleeve over its entireaxial length. In any event, the stent should contact sleeve 54 over atleast its entire medial region. Thus, there is no tendency in the stentto travel with exterior catheter 18 as this catheter moves axiallyrelative to catheter 26. Rather, the stent remains essentially fixed inthe axial direction relative to catheter 26. As a result, the axialposition of interior catheter 26 serves as a reliable indication of thelocation of stent 66, not only before deployment, but throughout most ofthe deployment procedure.

An adhesive layer 68 on the exterior surface of retaining sleeve 54 ofcourse further insures that stent 66 remains axially fixed relative tothe interior catheter. It has been found that adhesive is not necessarywhen deploying a stent of open weave or mesh construction over itsentire length. Friction due to the lower durometer of the retainingsleeve, alone, has been found sufficient to anchor the stent. However,when a silicone or other polymeric film covers the stent medial region,the adhesive is a key factor, in combination with the low durometer, inretaining the stent during external catheter withdrawal.

As shown in FIG. 3, stent 66 is in a reduced-radius and axiallyelongated configuration. The stent is compressed into this configurationdue to the external radial force provided by exterior catheter 18. Whenthe exterior catheter is withdrawn, thus removing the external force,stent 66 assumes a normal or relaxed configuration shown schematicallyin FIG. 4. More particularly, a medial region 70 of the stent assumes adiameter of about 20 mm, and opposite end regions 72 and 74 of the stentassume a diameter of about 30 mm.

Hub 24 is fixed to exterior catheter 18, and has an opening toaccommodate interior catheter 26 such that the interior catheter isslidable axially relative to hub 24. Hub 40 has an opening formedtherethrough, to accommodate guidewire 44.

An annular sleeve detent 76 surrounds the proximal region of interiorcatheter 26, between hubs 24 and 40. When positioned as shown in FIG. 1,retaining sleeve 76 surrounds the interior catheter and abuts the hubsto prevent any substantial movement of the interior catheter axiallyrelative to exterior catheter 18. Sleeve 76 thus functions as a safetydetent, preventing premature deployment of the stent. Sleeve detent 76has a lengthwise slit, and thus is easily removed from proximal region32 for stent deployment.

Deployment of stent 66 within the esophagus is considered appropriatewhen a tumor, lesion or other stricture has constricted the esophagealpassageway to a diameter less than about 15 mm. This represents a severeconstriction in light of the normal passageway diameter of about 22 mm.Deployment begins by oral insertion and positioning of guidewire 44,using an endoscope (not shown) in a manner well known in connection withtreating not only the esophagus but other body lumens, e.g. arteries.The guidewire catheter has a diameter of about 0.035-0.042 inches. Oncethe guidewire has been properly positioned, the endoscope is withdrawn.

Next, deployment device 16, including stent 66 radially compressed asshown in FIG. 3, is inserted over guidewire 44 and thus is directedtoward the desired treatment location as it is moved distally.Eventually, distal tip 28 of the device encounters the esophagealstricture. At this point, the deployment device is firmly but carefullymoved further in the distal direction, to utilize distal tip 28 todilate the region of the stricture. Once the distal tip has entered theregion, distal transition region 52 and mid-portion 48 of theenlargement feature are used to further dilate the region of thestricture, eventually to the point where the distal region of exteriorcatheter 18 is passed through the region of the stricture. Thus,according to one feature of the present invention, the stent deliverydevice also dilates the region of the esophageal stricture and noseparate dilating tool is required.

With the distal end of the exterior catheter past the stricture, stentdeployment is initiated. More particularly, with interior catheter 26held substantially fixed, hub 24 is manipulated by hand to withdrawexterior catheter 18 in the proximal direction. When hub 24 encounterssegments 34 along the proximal region 32 of the interior catheter, thedistal end of the exterior catheter is near the distal end of stent 66,meaning that deployment is about to begin. Before further withdrawal ofthe exterior catheter, it is advisable to re-examine the stent position,to insure that medial region 70 of the stent is aligned with thestricture, represented in FIG. 5 by a tumor 78 in esophageal wall tissue80. With stent 66 properly aligned, exterior catheter 18 is withdrawnproximally until hub 24 encounters segment 36. As shown in FIG. 5, bythe time the hub encounters segment 36, distal end region 72 of stent 66is released from the exterior catheter and radially self-expands untilit encounters tissue 80.

FIG. 6 illustrates further withdrawal of exterior catheter 66, to thepoint where hub 24 encounters marked segment 38. This corresponds torelease of stent 66 over its distal region and medial region, i.e.roughly two-thirds deployment. One of the advantages of retaining sleeve54 is that even at this advanced stage, it remains possible to recoveror retract stent 66 by moving exterior catheter 18 distally relative tointerior catheter 26. Such stent recapture occasionally is necessary, inorder to reposition stent 66 relative to the esophageal stricture. Moregenerally, the stent is virtually always retractable, even when amajority of its axial length is released. With the stent retaining meansof the present invention, stents have been found to be retractable afterup to 80 percent deployment.

FIG. 7 illustrates full withdrawal of exterior catheter 18 to completelyrelease stent 66, corresponding to proximal movement to the point wherehub 24 is at the proximal end of proximal segment 38. Stent 66 isradially expanded (and axially shortened) over its entire length,although not expanded to its normal, relaxed configuration. Rather, thestent expands only until the constraining force of esophageal tissue 80and the remaining residual force in the stent reach an equilibrium. Inthe equilibrium state, stent 66 has a diameter substantially larger thanthe diameter of enlargement feature 46, in particular its mid-portion.Accordingly, interior catheter 26 can be withdrawn proximally throughthe expanded stent. Proximal transition region 50 further insuresagainst the possibility of enlargement feature 46 being caught duringattempted withdrawal, either by stent 66 or a stricture in theesophagus. However, as a precaution against this event, the physiciancan advance exterior tubing 18 distally through the deployed stent untilits distal end once again surrounds the enlargement feature as shown inFIG. 1.

FIG. 8 illustrates a proximal withdrawal of enlargement feature 46 anddistal tip 28 past stent 66. Withdrawal of the delivery tool is followedby withdrawal of guidewire 44, unless the guidewire is retained forguiding another tool, e.g. an endoscope, into the esophagus.

FIG. 9 illustrates the radial compression of stent 66 by exteriorcatheter 18 to press the stent into surface engagement with restrainingsleeve 54. FIG. 10 is a view similar to FIG. 9, but showing analternative deployment device in which several strips 82, elongate inthe axial direction, are spaced apart angularly in an array about aninterior catheter 84. Like sleeve 54, the strips are constructed of amaterial having a substantially lower durometer than the catheters. Thestrips are secured to the interior catheter and, if desired, areprovided with adhesive coatings along their radially outward surfaces,as indicated at 86.

While stent 66 is satisfactory in many respects, it is unsuitable fortreatment of certain cancerous tissue in the esophagus. Such tissue isnot as strong as healthy esophageal tissue, and thus is subject torupture or other damage from an excessively rapid and forceful expansionof a conventional open weave stent. The stent is subject to tumoringrowth due to its open weave construction. Further, points or edges atthe opposite ends of the stent may perforate the esophageal wall.

A prostheses or stent 90, shown in FIG. 11, is constructed to addressall of these concerns. Like stent 66, stent 90 is of mesh or open weaveconstruction, comprised of multiple braided and helically wound strands.Stent 90 has a medial sleeve or region 92, a distal cuff 94 and proximalcuff 96. The proximal and distal ends of the stent are directed radiallyinward, as indicated at 98 and 100. When stent 90 is in its relaxed ornormal configuration as shown in the figure, medial region 92 has adiameter of about 20 mm, and the cuffs have a diameter of about 30 mm.The filaments forming the stent, preferably of a body compatiblestainless steel, are about 0.22 mm or less in diameter. As seen in FIG.11 (and also in FIGS. 15 and 16), the axial length of the medial region92 is on the order of about one-third of the axial length of the stent90.

While cuffs 94 and 96 are open, medial region 92 is circumscribed, i.e.completely covered, with a continuous polymeric film, preferablysilicone. The silicone film is applied by dip coating of stent 90, inwhich event the film initially covers one of the cuffs, and is removedfrom that cuff prior to using the stent. The preferred thickness of thesilicone film is in the range of 0.003-0.01 inches (0.075-0.25 mm), andis controlled primarily by the number of dip coating applications. Morespecifically, from three to five dip coatings result in a thicknesswithin the preferred range.

The silicone film is elastic, and thus is radially self-expanding likethe remainder of stent 90. However, the silicone reinforces the medialregion such that it has a much greater restoring force than the openweave portions of the stent. In particular, while cuffs 94 and 96 tendto recover virtually instantaneously from a radially compressedconfiguration, a tumor would inhibit their recovery. Medial region 92recovers against a tumor, although it has been observed to take 24 hoursfor recovery. It has been found that the recovery rate of the medialregion 92 can be controlled by controlling the thickness of the siliconefilm.

The gradual recovery rate of the medial region against tumors affordsseveral advantages which make stent 90 particularly well suited fortreating esophageal strictures. Certain advantages arise from the coatedmedial region itself, and other advantages arise from the combination ofthe medial region with cuffs 94 and 96. Considered alone, medial region92 provides an effective barrier to tissue ingrowth, because of thecontinuous silicone film. The gradual recovery of medial sleeve 92, fromthe radially compressed state when the stent is deployed, substantiallyreduces the chance that weakened cancerous tissue will be harmed duringstent radial self-expansion. While a recovery rate of about one hourwould significantly reduce most of the risk, the observed recovery rateof 24 hours is highly preferred. A further advantage arises from thefact that the residual force along the medial region is greater than theresidual force along the more rapidly expanding cuffs. As a result, themaximum radial dilating force is provided along that portion of stent 90aligned with the esophageal stricture.

As mentioned above, cuffs 94 and 96 radially expand rapidly upon theirrelease from a stent confining means such as exterior catheter 18. Thus,the cuffs rapidly contact and reach equilibrium with healthy tissue ofthe esophageal wall. Residual force in the cuffs at equilibrium is muchless than the residual force along medial region 92. As a result, cuffs94 and 96 readily conform to changes in the esophageal wall duringswallowing and other convulsions of the esophagus. Thus, the cuffs areparticularly effective in resisting either proximal or distal migrationthe stent. The open weave construction of the cuffs does not give riseto the problem of tumor ingrowth, since medial region 92 is aligned withthe stricture, while the cuffs engage healthy tissue.

Yet another advantage of the silicone film is that it providesreinforcement along medial region 92, enabling the stent to beconstructed with a reduced braid angle. The braid angle is measured,based on the filament incline from the axial dimension of the stent.FIGS. 12 and 13 illustrate a high braid angle and a low braid angle,respectively. In each case, the stent is oriented with its axial lengthin the horizontal direction. Heretofore, 90 degrees has been considereda lower practical limit for the braid angle of a mesh or open weavestent. Employing the silicone film, however, enables a reduction of thebraid angle to as low as 70 degrees, as illustrated in FIG. 13. Theadvantage of a lower braid angle resides in the fact that the braidangle determines the ratio of stent axial shortening to radial increase,as the stent self-expands. With a reduced braid angle, there is lessaxial shortening for a given radial expansion. Due to the reduced axial"drift", the stent can be more accurately positioned within body lumensduring its deployment.

FIG. 14 illustrates a mandrel 102 particularly well suited for formingstent 90. Mandrel 102 includes a central shank 104, enlargements 106 and108 on opposite sides of the shank, and end portions 110 and 112. Toform the stent, the individual filaments or strands are wound in helicalfashion to form an open weave cylinder. The cylinder is placed uponmandrel 102 and heated to a temperature in the range of from about800-1,000 degrees F. The filaments, when cooled, retain the shape of themandrel. Portions of the stent formed along the outer ends of themandrel are trimmed, leaving the inwardly directed ends 98 and 100.

FIGS. 15 and 16 schematically illustrate stent 90 after its deploymentin the esophagus. An esophageal wall 114 includes a tumor 116. Using adevice such as device 16, stent 90 is deployed as above explained.Medial region 92 of the stent is aligned with the tumor, and cuffs 94and 96 are aligned with healthy portions of the esophageal wall 114proximally and distally of tumor 116. The cuffs expand into engagementand equilibrium with esophageal wall 114 substantially immediately afterdeployment. Medial region 92, while it may engage tumor 116, remainsradially reduced.

FIG. 16 illustrates stent 90 one day after deployment. Medial region 92has recovered, and presses against tumor 116 to maintain the esophagealpassage along the stricture. The diameter of medial region 92 atequilibrium is likely to be greater than two-thirds of the cuff diameterat equilibrium, because of the greater residual force due to thesilicone film.

FIG. 17 illustrates another alternative stent 120 particularly suitedfor esophageal placement near the stomach, more particularly when aflared distal end or lower end 122 of the stent is near or protrudinginto the stomach, e.g. to treat a stricture near the stomach.Accordingly, stent 120 includes a distal region 124 circumscribed with acontinuous silicone film, and a proximal cuff 126 of mesh or open weaveconstruction. The proximal end 128 of the stent is inclined inward, toavoid the chance for esophageal perforation. Stent 120 can be deployedwith a tool substantially identical to deployment device 16.

Thus, in accordance with the present invention, a radiallyself-expanding stent includes a barrier region circumscribed by asilicone film to reduce tumor ingrowth, in combination with a fixationregion of open weave construction. The stent is resistent to migrationand to tumor ingrowth, and can be configured to recover gradually alongits barrier region after deployment, to minimize harm to weakened,cancerous tissue. The device for deploying the stent incorporates adilation tip and a further dilation feature proximally of the tip, toeliminate the need for a separate esophageal dilating tool. Duringdelivery and deployment, the stent surrounds and is radially compressedagainst a low durometer stent restraining sleeve. This fixes the stentaxially with respect to an interior catheter of the deployment device,for enhanced accuracy in stent positioning and enhanced ability torecover or retract a partially deployed stent.

What is claimed is:
 1. A device for fixation in a body lumen,including:a tubular stent of open weave construction having an axiallength and a predetermined normal configuration and being radiallycompressible to a reduced-radius configuration to facilitate an axialinsertion of the stent into a body lumen for delivery to a treatmentsite within the body lumen; and a continuous elastomeric film formedaxially along the stent and having an axial length, said continuous filmcircumscribing the stent over substantially the entirety of said axiallength to define a barrier region of the stent to substantially preventgrowth of tissue through the stent along the barrier region, said axiallength of said film being at least about one-third the axial length ofthe stent; and wherein a portion of the open weave construction of thestent is substantially free of the continuous film to provide a fixationregion of the stent for positively fixing the stent within the bodylumen at the treatment site, by radial expansion of the stent into asurface engagement with a tissue wall segment defining the body lumen.2. The device of claim 1 wherein:the stent is elastic, tending to assumethe reduced-radius configuration in response to the application of anexternal force, and tending to assume the normal configuration in theabsence of the external force.
 3. The device of claim 2 wherein:the filmreinforces the stent along the barrier region.
 4. The device of claim 3wherein:the film is formed of silicone.
 5. The device of claim 3wherein:the fixation region of the stent tends to exert a lowerrestoring force in its return toward the normal configuration, ascompared to the barrier region of the stent, upon removal of theexternal force.
 6. The device of claim 5 wherein:the barrier regionrequires at least one hour to return toward the normal configurationwhen encountering a tumor.
 7. The device of claim 2 wherein:the stentcomprises a mesh formed of braided helical strands.
 8. The device ofclaim 7 wherein:a braid angle, defined as the angle between twointersecting helical strands and encompassing a longitudinal axis of thestent, is approximately 70 degrees.
 9. The device of claim 2wherein:said fixation region is comprised of a proximal cuff and adistal cuff, and the barrier region is comprised of a medial sleeve ofthe stent between the proximal and distal cuffs.
 10. The device of claim9 wherein:the stent is formed of braided helical strands, with oppositeends of the strands at proximal and distal ends of the stent bentradially inward.
 11. The device of claim 1 wherein:the barrier regionhas a diameter less than the diameter of the fixation region when thestent is in the normal configuration.
 12. The device of claim 1wherein:said continuous film reinforces the stent along the barrierregion.
 13. A device for fixation in a body lumen, including:a flexibletubular stent having a predetermined normal configuration and beingradially elastically compressible responsive to the application of anexternal force to a reduced-radius configuration to facilitate an axialinsertion of the stent into a body lumen for delivery to a selectedtreatment site in the body lumen; said stent, following removal of saidexternal force, tending to radially self-expand into a surfaceengagement with a tissue wall segment defining the body lumen, therebyto fix the stent within the body lumen; and an elastically deformablereinforcement sleeve means integral with the stent, disposed axiallyalong the stent and substantially surrounding the stent over areinforced region of the stent, said reinforced region requiring atleast one hour to return to the normal configuration after removal ofthe external force; wherein a portion of the stent is substantially freethe reinforcement sleeve means to provide a fixation region of thestent, and the fixation region, as compared to the reinforced and withless restoring force region, tends to radially self-expand with lessrestoring force upon removal of said external force.
 14. The device ofclaim 13 wherein:the elastic reinforcing means comprises a polymericfilm.
 15. The device of claim 14 wherein:the polymeric film is asilicone film.
 16. The device of claim 13 wherein:the fixation region iscomprised of proximal and distal cuffs, and the reinforced region iscomprised of a medial region of the stent between the proximal anddistal cuffs.
 17. The device of claim 16 wherein:the proximal and distalcuffs have diameters larger than the diameter of the medial region whenthe stent is in the normal configuration.
 18. A device for fixation in abody lumen, including:a tubular elastic stent of open weave constructionhaving a predetermined normal configuration and being radiallycompressible to a reduced-radius configuration in response to theapplication of an external force to facilitate an axial insertion of thestent into a body lumen for delivery to a treatment site within the bodylumen, and tending to assume the normal configuration in the absence ofthe external force; and a continuous elastic polymeric film formedaxially along the stent and circumscribing the stent over a barrierregion of the stent to substantially prevent growth of tissue throughthe stent along the barrier region, said film reinforcing the stentalong the barrier region; and wherein a portion of the stent issubstantially free of the continuation film to provide a fixation regionof the stent for positively fixing the stent within the body lumen atthe treatment site, by radial expansion of the stent into a surfaceengagement with a tissue wall segment defining the body lumen, with thefixation region of the stent tending to exert a lower restoring force inits return toward a normal configuration, as compared to the barrierregion of the stent, upon removal of the external force.
 19. A devicefor fixation in a body lumen, including:a tubular elastic stent of openweave construction tending to assume a predetermined normalconfiguration in the absence of an external force and being radiallycompressible to a reduced-radius configuration in response to anapplication of the external force to facilitate an axial insertion ofthe stent into a body lumen for delivery to a treatment site within thebody lumen; and a continuous elastomeric film formed axially along thestent and having an axial length, said continuous film circumscribingthe stent over substantially the entirety of said axial length to definea barrier region of the stent to substantially prevent growth of tissuethrough the stent along the barrier region; wherein a portion of thestent is substantially free of the continuous film to provide a fixationregion of the stent for positively fixing the stent within the bodylumen at the treatment site, by radial expansion of the stent into asurface engagement with a tissue wall segment defining the body lumen.20. The device of claim 19 wherein:said fixation region, as compared tothe barrier region, tends to radially self-expand with less restoringforce upon removal of the external force.
 21. The device of claim 19wherein:said barrier region requires at least one hour to return to thepredetermined normal configuration after removal of the external force.22. The device of claim 19 wherein:said tubular elastic stent has anaxial length, and the axial length of the continuous elastomeric film isat least about one-third of the axial length of said tubular elasticstent.
 23. A device for fixation in a body lumen, including:a tubularstent of open weave construction having a predetermined normalconfiguration and being radially compressible to a reduced-radiusconfiguration to facilitate an axial insertion of the stent into a bodylumen for delivery to a treatment site within the body lumen; and acontinuous elastomeric film formed axially along the stent and having anaxial length, said continuous film circumscribing the stent oversubstantially the entirety of said axial length to define a barrierregion of the stent to substantially prevent growth of tissue throughthe stent along the barrier region; wherein a portion of the stent issubstantially free of the continuous film to provide a fixation regionof the stent for positively fixing the stent within the body lumen atthe treatment site, by radial expansion of the stent into a surfaceengagement with a tissue wall segment defining the body lumen; andwherein the barrier region and the fixation region have respective firstand second diameters when the stent is in the predetermined normalconfiguration, with said first diameter being less than the seconddiameter.
 24. The device of claim 23 wherein:said tubular stent has anaxial length, and the axial length of the continuous elastomeric film isat least about one-third of the axial length of said tubular stent. 25.The device of claim 23 wherein:said tubular stent is radiallyelastically compressible under an external force, and fixation region,as compared to the barrier region, tends to radially self-expand towardthe predetermined normal configuration with less restoring force uponremoval of the external force.
 26. The device of claim 25 wherein:saidbarrier region requires at least one hour to return to the predeterminednormal configuration after removal of the external force.